Dual tank systems are oftentimes employed in a hydraulic circuit for an earthworking vehicle to continuously communicate an adequate supply of hydraulic fluid to work implements employed in such circuit. Each of the tanks normally contains a substantial pocket of air therein to induce an undesirable aeration of the hydraulic fluid contained therein. A system of this type is disclosed in U.S. Pat. No. 3,604,205, assigned to the assignee of this application. U.S. Pat. No. 3,222,866 also discloses a dual tank system wherein a rather complicated circuitry is utilized in an attempt to maintain a lower tank in a filled condition.